Microsecond-pulse glow discharge atomic emission

A microsecond pulsed glow discharge was produced with high pulse magnitude and small duty cycle. Time resolved emission and absorption spectroscopy was applied to study the processes of atomization, excitation and ionization in the glow discharge. Experimental results show that, without overheating the sample, the emission peak intensity is several orders greater than that obtained in the conventional dc mode. This implies that a much more intense plasma is generated during pulsed "on" region.     

Spatially-resolved observation of glow discharge plasma for atomic emission spectrometry.

An imaging spectrograph equipped with a CCD detector was employed to measure two-dimensional emission images from a glow discharge plasma in atomic emission spectrometry. The emission images at Zn I 334.50 nm for a zinc sample and at Cu I 324.75 nm for a copper sample could be obtained. Their emission intensities were not uniform in the radial direction of the plasma region but became weaker at larger distance from the central zone. The two-dimensional distribution would result from a spatial variation in the excitation efficiency of the plasma and thus provide useful information for understanding the excitation processes occurring in the plasma.     

A glow discharge device for atomic emission spectrometry of microliter solution samples

A novel glow discharge device designed specifically for solution analysis is described. The detection limits obtained are comparable to those obtained with demountable hollow cathode lamps, but with better precision. Rotational and excitation temperatures are examined as functions of fill gas pressure and discharge current. A sputtering constant is presented and the technique for measuring this parameter is described.     

Modeling of glow discharge optical emission spectrometry: Calculation of the argon atomic optical emission spectrum

The optical emission spectrum of the argon atomic lines in a glow discharge is calculated, using a collisional–radiative model for argon, which was recently developed (A. Bogaerts et al., Collisional–radiative model for an argon glow discharge, J. Appl. Phys., vol. 84, No 1, 1998). It is shown that the lines corresponding to 4p→4s transitions clearly dominate the spectrum. They are, however, not responsible for the characteristic visible light in the glow discharge, because they are lying between 700 and 1000 nm, which is mainly in the near infrared. The characteristic blue light of the glow discharge is caused by the lines corresponding to 5p→4s transitions (lying in the blue–violet part of the spectrum). Beside these two most important line groups (the so-called `red' and `blue' lines) a large number of other lines are present, making the entire argon spectrum quite complex. The calculated spectrum is compared with experimental spectra from the literature, and excellent qualitative agreement is obtained.The calculated spatial distributions of optical emission lines originating from low excited levels (i.e., 4p, 3d, 5s, 5p, 4d, 6s) show a maximum in the cathode glow, caused by fast argon ion and atom impact excitation, to these levels, and a second maximum in the beginning of the negative glow, due to electron impact excitation. The maximum in the cathode glow is very pronounced for lines originating from the 4p levels, which is in agreement with experimental observations. The higher excited levels are not populated by fast argon ion and atom impact excitation but only by electron impact excitation; hence, lines originating from these levels exhibit only a maximum in the beginning of the negative glow.     

Design and characterization of a planar magnetron radiofrequency glow discharge source for atomic emission spectrometry

A planar magnetron radio-frequency-powered glow discharge source has been constructed and characterized. Electrical behavior, sputtering rates, and emission properties of the source have been studied with both conducting and insulating samples over a pressure range of 0.05 to 0.6 Torr, and over a forward-power range between 30 and 120 W. The bias voltage showed little or no dependence on power or on pressure between 0.2 and 0.6 Torr. However, at lower pressures there was a sharp increase in the voltage as pressure was dropped, signaling a change in the operational mode of the discharge. The magnetron source proved to have much higher sputtering rates for both conducting and insulating samples than a similar source without a magnet; the highest sputtering rates were found at 0.05 Torr. The dependence of emission on pressure was similar to that of previously described d.c. magnetron sources. Detection limits ranged from 1 to 50 ppm for elements in a conducting matrix.     

Hydrogen effects on copper,zinc and nickel atomic emission lines in argon radiofrequency glow discharge optical emission spectrometry

The effect of hydrogen (0.5%, 1% and 10% v/v) added to the argon plasma gas on the emission spectra of selected atomic lines for copper, zinc and nickel has been studied by radiofrequency glow discharge optical emission spectrometry (rf-GD-OES). Conductive homogeneous samples containing different concentrations of the elements under study in different matrices have been investigated. Results show different trends of the emission intensity lines with increasing hydrogen concentration in the rf-GD, depending on the line characteristics. In most cases, the emission yields of the lines under study did not change or increased when hydrogen was added to the discharge (no decreases were observed). The emission yields of certain lines showed much higher increases than other lines of the same element (for example, lines 213.86 nm of Zn and 231.10 nm of Ni). Our experiments indicate that such notorious increases could be related with the possible decrease of the self-absorption when hydrogen is added to the discharge. Overall, the results obtained for the emission yield changes of certain lines of a given element in different matrices (with different analyte content) showed that while for resonance emission lines very notorious increases are observed, the values for non-resonance lines do not change significantly (specially if the matrices employed are similar).     

A photon counting dynamic digital lock-in amplifier for background suppression in glow discharge atomic emission spectrometry

A photon counting dynamic digital lock-in amplifier, (PC-DDLIA), has been developed for the suppression of Ar lines in glow discharge lamp atomic emission spectrometry, (GDL-AES). The experimental set-up consists of a Grimm-type GDL, a prism-type scanning monochromator, photon counting electronics, an Apple Ile computer with an interface card and a computer controllable high voltage power supply. The photon counting electronics are designed to convert the photon pulses to logic pulses. A discriminator is used to reject pulses below a threshold level. The high voltage power supply is modulated with a square waveform generated from DAC and photon pulses are counted synchronously by the timer/counter chip, versatile interface adaptor (VIA-6522) on the interface card of computer. The data are analyzed in two steps. In the “learn mode”, the GDL is modulated with a square waveform between 370 and 670 V and two spectra consisting of only Ar lines are obtained in a spectral window between 287.1 and 290.0 nm. A new modulation waveform is computed from these spectra which yields two overlapped spectra when the PC-DDLIA is scanned over the same spectral window. In the “analysis mode” of data acquisition, a target material with the analyte element(s) in it is used and the spectrometer is scanned with a dynamically varying rectangular waveform over the same spectral window. The net spectrum consists of pure atomic lines free from any Ar lines. The detection limit for the determination of Si (288.2 nm) in the presence of interfering Ar lines (288.1 and 288.4 nm) is found to be 0.083%, whereas suppression of Ar lines over the same spectral window lowers the detection limit to 0.013%.     

Determination of Hg by on-line separation and pre-concentration with atmospheric-pressure solution-cathode glow discharge atomic emission spectrometry

A simple and sensitive method to determine Hg²⁺ was developed by combining solution-cathode glow discharge atomic emission spectrometry (SCGD-AES) with flow injection (FI) based on on-line solid-phase extraction (SPE). We synthesized l-cysteine-modified mesoporous silica and packed it in an SPE microcolumn, which was experimentally determined to possess a good mercury adsorption capacity. An enrichment factor of 42 was achieved under optimized Hg²⁺ elution conditions, namely, an FI flow rate of 2.0 mL min⁻¹ and an eluent comprised of 10% thiourea in 0.2 mol L⁻¹ HNO₃. The detection limit of FI–SCGD-AES was determined to be 0.75 μg L⁻¹, and the precision of the 11 replicate Hg²⁺ measurements was 0.86% at a concentration of 100 μg L⁻¹. The proposed method was validated by determining Hg²⁺ in certified reference materials such as human hair (GBW09101b) and stream sediment (GBW07310).     

Ultrasensitive determination of mercury by solution anode glow discharge atomic emission spectrometry coupled with hydride generation

An innovative method for the ultrasensitive detection of mercury by solution anode glow discharge atomic emission spectroscopy (SAGD-AES) coupled with hydride generation (HG) was first investigated. In this method, the mercury vapor generated by the HG was transmitted to the SAGD through the miniature hollow tungsten tube for excitation and detected by a miniaturized spectrograph. A thorough parametric evaluation of the HG and SAGD system was performed, including the type and concentration of carrier acid, He flow rate, concentrations of NaBH₄, discharge current and discharge gap. Under optimal operating conditions, the detection limit for Hg²⁺ achieved 0.03 μg/L, with a relative standard deviation of 1.1% at the Hg²⁺ concentration of 5 μg/L. Moreover, the correlation coefficient of the calibration curve was 0.9996 in the range between 0.1 and 10 μg/L. The accuracy and practicability of HG-SAGD-AES were verified by measuring GBW09101b (human hair), GBW10029 (fish), soil and rice samples. The results showed good agreement with the certified values and values from direct mercury analyzer (DMA).     

Solid sample atomic absorption analysis after glow discharge sputtering

Summary The use of the Atomsource atomizer and a double-beam/two-channel AA instrument shall be described at first. It seems that this relatively new combination of sputtering chamber and atomic absorption measurement needs a long time to be applied. Both these techniques are not used normally in one laboratory by the same operators. May be the different aims to analyse solutions by AA and solids by glow discharge sputtering makes it more difficult to see the advantages. These are given, especially in the case of analysis of metals and other conducting materials, by the short time needed for sputtering and the accuracy, simplicity, and flexibility caused by AA meausurements. In addition, AA becomes available to determine elements like B, Ce, La, Nb or Zr much better than before.     

Electrical and optical characteristics of a radio frequency glow discharge atomic emission source with dielectric sample atomization

A parametric study has been conducted on a radio frequency powered glow discharge atomic emission spectrometry (rf-GD-AES) source to evaluate its performance in the direct analysis of non-conducting solid materials. These experiments include both the emission and electrical characterization of this system with respect to discharge power, pressure, limiting anode orifice diameter, and sample size. The rf-GD-AES source has been demonstrated to operate interchangeably between conducting and non-conducting sample materials; however, the energy dissipated within the plasma appears to be reduced with the dielectric samples, resulting in lower emission intensities and sputtering rates. The power losses have also been found to be a function of the size, or thickness, of the sample materials. Despite these limitations of the system, preliminary emission data demonstrate that the rf-GD-AES system can be successfully employed in the direct, trace analysis of non-conducting sample materials.     

Direct analysis of glass powder samples by radio frequency glow discharge atomic emission spectrometry (rf-GD-AES)

A method is described for the elemental analysis of glass powder samples by rf-GD-AES. Glass powder samples were pressed without binder to form sample disks. A brass sample holder was designed to hold the pellet onto the source and provide a good vacuum seal. Sample preparation conditions and particle sizes are shown to influence spectral characteristics and plasma stabilization times. The discharge operating parameters were optimized based on both raw analyte signal intensity (S) and signal-to-background ratio (S/B), the latter was found more useful in terms of sample-to-sample precision and quantification. A NIST Standard Reference Material (SRM 89 Lead-Barium Glass) was used to evaluate the method. The limits of detection for trace components ranged from 1–10 g/g for several elements, depending on the concentrations of the analytes in the SRM. Sample-to-sample reproducibilities were better than 10% RSD and linear calibration curves were obtained using either the Si (I) optical emission as an internal standard or the individual analyte's S/B characteristics.     

The design and characteristics of direct current glow discharge atomic emission source operated with plain and hollow cathodes

A compact direct current glow discharge atomic emission source has been designed and constructed for analytical applications. This atomic emission source works very efficiently at a low-input electrical power. The design has some features that make it distinct from that of the conventional Grimm glow discharge source. The peculiar cathode design offered greater flexibility on size and shape of the sample. As a result the source can be easily adopted to operate in Plain or Hollow Cathode configuration. I-V and spectroscopic characteristics of the source were compared while operating it with plain and hollow copper cathodes. It was observed that with hollow cathode, the source can be operated at a less input power and generates greater Cu I and Cu II line intensities. Also, the intensity of Cu II line rise faster than Cu I line with argon pressure for both cathodes. But the influence of pressure on Cu II lines was more significant when the source is operated with hollow cathode.     

A miniature planar magnetron glow discharge source for analysis of submicroliter volume aqueous samples using atomic emission spectroscopy

A miniature planar magnetron glow discharge source with a chamber volume of 60 ml has been designed and evaluated for the analysis of less than 1 μl of aqueous samples by atomic emission spectroscopy. Limits of detection for magnesium, silver, boron, europium and copper in the presence of a magnetic field are observed to be 3 to 40 times lower than for the source without a magnetic field when the measurements are made under the compromised discharge conditions for each type of source. Emission intensity in the presence of the magnetic field is found to increase as a square function of the discharge current. The improved detection limits for the magnetically enhanced glow discharge source are attributed to the increased current density of the discharge in the presence of the magnetic field which formed a plasma ring localized above the cathode surface. An RSD in the range 15–25% is observed for these measurements.     

Measuring metal substrate roughness with glow discharge optical emission spectrometry

Although there are many methods to evaluate metal surface roughness, it is difficult to detect the substrate roughness of coated samples. Depth profile analysis (DPA) is proposed as a new method for the substrate roughness measurement, and glow discharge optical emission spectrometry (GDOES) becomes a candidate in substrate roughness measuring instruments. With this method, the typical roughness parameters R_a (arithmetic mean of the absolute deviation values of the roughness profile) and R_y (maximum value of consecutive peak and valley heights of the roughness profile along the sampling length) can be easily obtained. The principle of this method is discussed and the formulasof the principle are deducted in this paper. Electrodeposited zinc coating on copper substrate specimens is used as an example to explain the measuring process. Copyright © 2007 John Wiley & Sons, Ltd.     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material.     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material. Recieved: 22 December 1999 / Revised: 25 February 2000 / Accepted: 25 February 2000     

Design and initial characterization of a glow discharge atomic emission instrument for macro-scale elemental composition mapping of solid surfaces

An instrument intended for rapid, accurate, precise, macro-scale (i.e. up to many tens of square centimeters) elemental composition mapping of solid surfaces has been designed and constructed. The spatial resolution provided by the instrument, on the order of 1 mm at best, is coarse by today's standards but is appropriate for selected analytical problems. The instrument is based on a novel glow discharge atomic emission device capable of sustaining multiple discharges simultaneously. Each discharge exhibits atomic emission characteristic of the sample surface beneath it. Using Hadamard transform spatial imaging, the emissions are selectively multiplexed, and the individual emission intensities are recovered from the multiplexed data through matrix multiplication. In this publication, the instrument is described, and its performance for elemental composition mapping is demonstrated. The data indicate that internal standardization should be employed to reduce the likelihood of mapping errors.     

A contribution to the solution of the problem of quantification in surface analysis work using glow discharge atomic emission spectroscopy

The emission intensity from spectral lines has been studied in a Grimm-type glow discharge lamp (GDL). The variation in intensity of Ar I lines was investigated in order to exclude the influence of the sample sputtering rate. The variations in intensity of several analytical lines were then studied and compared with the sample sputtering rate. It was concluded that the sample atom number density in the plasma saturates with increasing voltage. An empirical intensity expression, taking into account the current, voltage and sample composition is presented. This expression was used for the determination of elemental concentrations in Cu based alloys, using a single steel reference sample as standard. An application of this procedure to a surface analysis problem is presented, and the results are compared with atomic absorption measurements. Good agreement was obtained, indicating that surface analysis data can be quantified in a simple and straightforward manner.     

Bias-current modulation technique of a radio-frequency glow discharge plasma for atomic emission analysis associated with a fast Fourier transform analyzer

A measuring method using a fast Fourier transform (FFT) analyzer is suggested to estimate the emission intensity from a radio-frequency (RF)-powered glow discharge plasma for atomic emission analysis. The FFT analyzer has an ability to disperse the components by frequency from an overall signal, and thus works as a selective detector in modulation spectroscopy. In the RF glow discharge plasma, a dc bias current can be introduced by connecting an external electric circuit with the discharge lamp, which predominantly enhances the emission intensities. Further, the bias current can be pulsated with a switching device to modulate the emission intensities, and then the modulated component was selectively detected with the FFT analyzer. This method greatly improved the data precision. The emission intensity of the Cu I 324.75-nm line in an Fe-based alloy sample containing 0.043 mass% Cu could be estimated with a relative standard deviation of 0.20%. The 3σ detection limits of Cu in Fe-based alloys could be obtained to be 2.3 × 10^− 6 mass% Cu for Cu I 324.75 nm and 6.8 × 10^− 6 mass% Cu for Cu I 327.40 nm.